Generally, during an X-ray imaging procedure while an X-ray is projected on a region of interest of a patient, it is inevitable that a radiation risk will be caused as a portion of the radiation dose will deposit in the patient's body when the X-ray is being projected passing through the patient's body toward a digital radiography (DR) device for producing a diagnostic signal or imaging a clinical image. Nevertheless, the dose of radiation that is deposit in the target area and the transmitted intensity of the X-ray can both be affected by the thickness of the patient in the parallel imaging direction, and moreover, the transmitted intensity of the X-ray is further related to the signal-to-noise ratio (SNR) of the image or the optical density (OD) on film. In short, a poor configuration of X-ray imaging parameters that are determined based on patient's body figures can have severe and adverse affect on the resulting image quality as well as the amount of radiation dose being deposited in the target area. As a common knowledge that the size difference between children and adult can be apparent, and that is also true for adult or children of the same age as they can be grown to be fat or skinny. Consequently, individual difference must be considered in the configuration of X-ray imaging parameters, including X-ray voltage (unit: kV), tube current (unit: mA) and exposure time (unit: s). Please refer to FIG. 1, which is a schematic diagram showing imaging results of different X-ray parameter configurations for patients of different body figures. In FIG. 1, the left image is an X-ray image of a patient of 91.2 kg in weight and is obtained by setting the X-ray tube voltage at 114 kV and the product of tube current and exposure time at 3.6 mAs, and the right image is an X-ray image of a patient of 48.9 kg in weight and is obtained by setting the X-ray tube voltage at 92 kV and the product of tube current and exposure time at 2 mAs.
Currently, the X-ray tube voltage, the tube current, and the exposure time are set generally based upon the radiologist's experience according to the patient body figure, the thickness of the target area and pathological features. That is, the two most importance parameters in X-ray imaging are determined solely by experience. However, following the advances in digital radiography, the detective quantum efficiency (DQE) of the current digital radiography device is enhanced and consequently the detective efficiency of the X-ray imaging system using the digital radiography device is enhanced as well. Thereby, a radiologist operating the X-ray imaging system can achieve an image of satisfactory quality using a comparative lower radiation dose than before and thus the risk of cancer from radiation exposure is reduced.
However, clinically radiologists still configure the X-ray tube voltage, the tube current, and the exposure time solely based upon their personal experiences according to the patient body figure and the thickness of the target area, which are achieved via operating a conventional automatic exposure control (AEC) device for controlling the radiation dose without considering the possible affection on image quality coming from the use of a current high performance digital radiography (DR) device. Therefore, even when a DR device of high DQE is available to radiologists, the possibility of taking high quality X-ray images using lower radiation doses is never being considered.
On the other hand, considering the diversity and complexity in the modern DR devices both technologically and materially, the whole parameter configuration process can be very time consuming and labor intensive as operators not only have to be familiar with the DQE performance of the imaging system, but also have to perform individual evaluation process for every patient so as to obtain an optimal imaging parameter for each individual patient. Thus, it is almost impossible for such process to be executed in the real-world hospitals as all real-world hospitals are constantly subjected to the heavy pressure of large amount of imaging workload waiting to be processed. In reality, many modern DR devices had been designed with a pre-scan function for reducing the dependence of the imaging process on the radiologist's experience in view of setting up optimal tube voltage and the product of tube current and exposure time. Although this method is more objective, but it can still be troubled by the shortcoming of excess radiation dose.
Please refer to FIG. 2, which is a schematic diagram showing an automatic expose control (AEC) unit for a conventional DR device. As shown in FIG. 2, the AEC unit is equipped with one or multiple radiation dosimeters, whereas on the upper left shows an AEC chamber 52 with five channels and on the upper right shows AEC chambers 54 of three channels. Operationally, the radiologist on duty will select the proper AEC channels according to the target region of each patient. Thus, the lower left image A1 shows a chest X-ray imaging of correct configuration, while the lower right image A2 shows another chest X-ray imaging of incorrect configuration where the image is overexposed. It is noted that the accessibility and availability of target region can be restricted by the position of AEC channels and the amount thereof as well.